1. Field of the Invention
The present invention relates to a printing apparatus which has a plurality of feeding units and supplies paper from a designated feeding unit to form an image, and a control method therefor.
2. Description of the Related Art
There is known an image forming apparatus which has a plurality of feeding units capable of setting sheets of different sizes. This image forming apparatus can print by feeding paper of a designated size or paper from a designated feeding unit in accordance with an instruction from a host computer. The image forming apparatus starts printing when a designated paper size matches the size of paper contained in a designated feeding unit. However, if these paper sizes do not match each other, the user is generally notified of an error or a warning message to request a necessary paper size. To solve this, Japanese Patent Laid-Open No. 9-323457 describes a method of changing the size of an image in accordance with the printing paper size when the size of paper contained in a designated feeding unit does not match that of an image to be printed. However, this method may not be able to provide a print result the user wants, because the size of a printed image differs from that of an original image.
As another method, for example, an error skip button is attached to an image forming apparatus. The user presses this button to ignore an error and forcibly print on paper of a designated size. Alternatively, it is proposed that when skipping an error, an alternative paper size is set for each paper size. When paper of the alternative size is available, the image forming apparatus prints on the paper; otherwise, it does not print (Japanese Patent Laid-Open No. 2002-036679).
However, in either method described above, the user cannot obtain the printed material he wants. A touch panel may be attached to select a feeding unit different from a selected one. In this case, the user can change the feeding unit by manipulating the touch panel, but the apparatus size increases, greatly raising the cost. To obtain a printed material the user wants without changing the feeding unit, it is necessary to “replace paper contained in a selected feeding unit with paper of a size of user's choice.” Even when paper of a requested size is contained in a feeding unit other than one designated by a print job, in order to change the feeding unit, it is necessary to “cancel a job once, set a feeding unit again by the print job, and print again.” This increases the amount of user work.